Konceptstudie av en kompakt Picker robot

Sammanfattning

Picker robots are often mounted close to each other above a conveyor belt. To be able to

pack robots even closer, it is desirable to reduce the footprint of the robot’s base. One way to

achieve this is to skew the arms of the robot which makes it possible to move them closer to

each other.

This Master Thesis has been carried out at ABB Corporate Research. The purpose is to

evaluate the benefits and drawbacks for the idea of making today’s Picker robot more

compact by skewing the arms. The concept is taken from the FlexPLP-Project in which a

similar robot named Deltapod was skewed. For the Deltapod robot a smaller footprint could

be achieved without reducing the workspace and robot stiffness too much. The evaluation is

made by investigating the changes of the following properties:

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The size of the workspace

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The size of the footprint

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The internal forces and joint torques required for different tasks

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Sensitivity against disturbance forces

The robots are modeled and investigated by using Modelica, which is an object oriented

language specifically designed for modeling large systems governed by differential algebraic

equations.

The skewing of the arms is based on keeping a characteristic angle of the structure. In

this way the stiffness of the robot is somewhat kept. The same approach was used for the

skewing of the Deltapod. The results show that skewing the robot is probably not the best

way to achieve a smaller footprint since the workspace shrinks faster than the footprint for

increasing skews. This problem was not encountered in the FlexPLP-Project. An explanation

for this phenomenon is given in the thesis. Other negative effects due to skewing are:

increasing internal forces and larger sensitivity against disturbance forces.

In addition to the rule of keeping the characteristic angle, two skewed Pickers based on

achieving the smallest possible footprint are also investigated. The resulting positioning of

the arms is interesting because it cannot be made without introducing a skew to the robot.

One of the robots is chosen to have a large workspace compared to the footprint, while the

other is chosen to keep the relationship between the workspace and the footprint. For both

the robots the disadvantages are larger internal forces, joint torques and sensitivity against

disturbance forces. Since the angles of the structure are not considered, the stiffness of the

robot can be expected to be worse than for the Picker.